Walmart has issued a warning to tech companies it does business with: don't use Amazon's cloud services.

Amazon has quickly emerged as the dominant player in cloud-based storage and computing power with its Amazon Web Services program.

Now, Walmart is turning up the heat as it aggressively invests in e-commerce.

The retailer is starting to tell technology companies it works with to stop using Amazon Web Services and move to competitors instead, The Wall Street Journal reported.

Amazon Web Services, known in the industry as AWS, is the dominant business for hosting websites and services, with a 44% share of the market, according to Synergy Research Group.

A spokesperson for Walmart confirmed to the Journal that Walmart pushed for its tech suppliers to use competitors, stating it wants to protect sensitive company data from a major competitor.

In a statement to the Journal, an Amazon spokesperson called Walmart's tactics an attempt to "bully" tech companies into using competitors, like Microsoft's Azure.

Matt Weinberger

The conflict comes at a time when Walmart and Amazon are battling for American dollars.

Amazon's purchase of Whole Foods Market will make the two almost directly competitive in the grocery business for the first time. Walmart is increasingly competitive with Amazon online as well, especially as it purchases more e-commerce companies like Jet.com, Modcloth, and Bonobos.

Jet competes with Amazon's broad retail bread and butter, while the women's fashion company Modcloth and men's clothing company Bonobos directly compete with the millennial online shoppers Amazon is trying to court with its Amazon Fashion initiative and Prime Wardrobe program.

Walmart itself prefers to use its own data centers, supplementing that with services from Amazon's emerging services competitors.